In this video series may be the way of teaching is different, but I can assure you that you will complete learning Bengali in 30 days.
I followed the book "Nije Paro" authorised by WB Education Rights written by famous writer "Shukhalata Rao". She was the daughter of Upendra Kishore Roychowdhury, and sister of Sukumar Ray, and aunt of famous scholar and director Satyajit Ray.
The teaching method established by WB Education Rights for the beginners as the First Book of Kindergarten Students.
http://www.youtube.com/user/virtualbengal